JLL, the US-based group, will pay £197m to King Sturge’s partners, creating a combined UK business with 2,700 employees.

The deal will combine King Sturge’s strengths in the UK regions and London, with JLL’s global reach, which is increasingly important as international investors pour into West End and City deals.

Christian Ulbrich, JLL’s European chief executive, said: “The obvious strategic and cultural fit between Jones Lang LaSalle and King Sturge makes this a logical and very attractive proposition for both firms.”

Richard Batten, joint senior partner at King Sturge, said the company believed it could only expand “beyond the traditional partnership model” and approached JLL because of the “cultural alignment” between the groups.

“This industry is far more fragmented than any of the other professional services sectors. If we moved, we wanted to do it early,” he added.

King Sturge’s 43 offices across Europe will be rebranded under the JLL name, with Mr Batten becoming executive chairman of the UK business and Andrew Gould retaining his position as JLL chief executive in the UK.

Mr Batten stressed that it was “a 50-50 merger”, with staff and income split 50-50, and played down the risk of key King Sturge agents leaving the business.

“Why would you?” he said. “This will be the number one business in the UK. Why would anyone want to leave? It is a great opportunity.”

The deal is expected to be completed on May 31, with £98m of cash paid up front to King Sturge’s partners and the rest paid out over five years.